1. Field of the Invention
This invention relates to an improved additive composition and process for the delignification of lignocellulosic material, such as wood, with an alkaline pulping liquor of the kraft, or sulfate, alkaline pulping process. More particularly, the invention relates to lignocellulosic material delignification with kraft pulping liquors containing a cyclic keto compound (preferably, anthraquinone), permitting enhanced yield. Specifically, the invention relates to an improvement of said process wherein said enhanced yield is achieved at reduced anthraquinone levels via the inclusion of a surfactant mixture comprising at least one alkyl alcohol alkoxylate and at least one polyoxyalkylene glycol ether of an ester of an acid selected from the group consisting of ricinoleic acid and 12-hydroxystearic acid
2. Description of the Prior Art
In the mid-1970s, a significant advance was made in the delignification of lignocellulosic material for the production of wood pulps upon the discovery of the benefits of using anthraquinone as a pulping additive to alkaline pulping liquors. Among the earliest public disclosures of such use of anthraquinone was U.S. Pat. No. 3,888,727, which taught treating lignocellulosic material with an alkaline pulping liquor containing anthraquinone sulfonic acid followed by oxygen delignification. More significantly, however, U.S. Pat. No. 4,012,280 taught that the poorer economics of the environmentally preferable soda pulping process could be improved to compete with the more environmentally offensive (in terms of odor) kraft process by incorporation of anthraquinone as a pulping additive. Although the benefits of increased yield of cellulosic pulp and increased rate of delignification (permitting lower energy consumption and higher throughput) were shown, the use of the improved, lower pollution potential soda process was not advanced. First, incorporating the relatively expensive anthraquinone in the soda process to make it productively competitive with the kraft process without antraquinone reduced its economic competitiveness. Second, the benefits of anthraquinone also were achieved in other (already more commercially employed) pulping process such as those employing kraft or polysulfide pulping liquors.
It was soon discovered, as disclosed in U.S. Pat. No. 4,213,821, that anthraquinone also benefited cooking wood chips in neutral sulfite pulping liquor (with a special case disclosed in U.S. Pat. No. 5,139,617), as well as in the alkaline pulping liquors. Methods for maximizing the benefits of anthraquinone were disclosed in U.S. Pat. Nos.: 4,127,439; 4,178,861; and 4,310,383. Also, due to anthraquinone's difficult-to-handle, water-insoluble, fine powder form, discoveries made to facilitate its dispersion in the pulping liquors are disclosed in U.S. Pat. Nos.: 4,248,663; 4,384,921; and 4,574,032. One disadvantage to anthraquinone use is its tendency to cause scaling problems in the cooking vessel. Methods to overcome this problem are disclosed in U.S. Pat. Nos.: 4,481,073 and 4,561,935. Finally, as a result of the relative high cost of anthraquinone, methods for recovering and reuse of the chemical are disclosed in U.S. Pat. Nos.: 4,197,168 and 4,310,383.
In spite of the aforementioned advances, there remains a need to improve the benefits of anthraquinone pulping (primarily reduction of energy and chemical requirements while improving yield) and to reduce its disadvantages (primarily cost and equipment scaling). One approach would be to replace a portion of the anthraquinone with an additive which provided some of the benefits of anthraquinone without providing the disadvantages which accompany its use.
Therefore, an object of this invention is to provide an improved pulping additive composition and process for delignification of a lignocellulosic raw material with a pulping liquor with anthraquinone for the production of a predetermined yield of cellulose pulp which composition and process permit the achievement of said yield, as well as other aforementioned benefits, with a reduced requirement of anthraquinone of at least 10%.